Internal-combustion engines fueled by gasoline, light oil, or the like and which are used in automobiles, motorcycles, agricultural machinery, industrial machinery, marine engines, and the like include those designed to improve fuel efficiency and output by directly injecting fuel into a cylinder using an injector (fuel injection valve).
Since such intra-cylinder direct-injection internal-combustion engines supply an injector with fuel pressurized to a higher pressure than in conventional systems and inject high-pressure fuel into a cylinder from the injector, a significant amount of energy (valve-opening electromagnetic force) is required for a valve-opening operation of the injector.
In consideration thereto, there is a recent trend towards an increase in a current applied to an electromagnetic load such as an injector used in an intra-cylinder direct-injection internal-combustion engine, resulting in an increase in the probability of failures in electromagnetic load circuits including an electromagnetic load and a driver circuit element. As a result, there is a growing demand for fragmentation and a higher degree of accuracy in failure diagnosis of electromagnetic load circuits.
An example of a circuit configuration including an injector for direct injection will be described with reference to FIG. 19.
An injector 20 that is an electromagnetic load has a positive terminal connected by a VB high-side driver 16 and a VH high-side driver 14, which are switch elements, to any of a power supply terminal 15 with standard voltage (battery voltage VB) and a high-voltage power supply terminal 13 with a boosting voltage VH and which is boosted to a higher voltage than the battery voltage VB. A diode 17 for backflow prevention is connected between the VB high-side driver 16 and the VH high-side driver 14. A negative terminal of the injector 20 is connected to a ground (GND) via a low-side driver 18 that is a switch element and a shunt resistance 22.
In this case, the side of a voltage terminal as seen from the electromagnetic load 20 will be referred to as a high side (upstream) and the side of the power supply ground (GND) as a low side (downstream).
The VB high-side driver 16, the VH high-side driver 14, and the low-side driver 18 are respectively driven-controlled by driver driving signals (c), (b), and (f) outputted by a VB high-side driver driving signal generating circuit 7, a VH high-side driver driving signal generating circuit 8, and a low-side driver driving signal generating circuit 9. The respective driver driving signal generating circuits 7, 8, and 9 generate control signals while being associated with each other by a logic signal outputted by a logic circuit 3 logic-operated by a control signal (a) of a microprocessor unit (MPU) 1.
A current detecting circuit 24 that detects a current flowing through the injector 20 is connected to the shunt resistance 22. A voltage detecting circuit 28 is connected to the current detecting circuit 24. The voltage detecting circuit 28 receives an input of a first reference voltage (h) from a first reference voltage generating circuit 26, and inputs a first voltage detection signal (i) to the logic circuit 3.
As illustrated in FIG. 20 as a shunt resistance conductive current (injector current), in a current waveform of the representative injector 20 for direct injection, the injector current is raised in a short period of time to a predetermined peak current stopping current using a boosting voltage VH during a peak current conduction period in an initial stage of conduction.
Next, in order to open a valve of the injector 20 for a predetermined amount of time, an injector current of a predetermined current value is held using a battery voltage by a switching operation of the VB high-side driver 16. At the end of injection, in order to swiftly close the valve of the injector 20, a conductive current drop of the injector conductive current is performed in a short period of time by the low-side driver 18 to interrupt the injector current (for example, refer to Patent Document 1).
Specifically, a rise in the control signal (a) outputted from the MPU 1 changes the VH high-side driver driving signal (b) to low and the low-side driver driving signal (f) to high, and a shunt resistance conductive current (g) that is equivalent to an electromagnetic load conductive current reaches a peak current threshold Ap. After reaching the peak current threshold Ap, the shunt resistance conductive current reaches a holding current threshold Ah1 and chopping of the VB high-side driver driving signal (b) occurs. After the elapse of a certain period of time, the first reference voltage (h) is switched and a transition to a holding current threshold Ah2 occurs. The injector 20 is controlled in the flow described above.
Moreover, in FIG. 20, reference character (d) denotes an electromagnetic load (injector) upstream voltage, (h) an electromagnetic load (injector) downstream voltage, and (i) a first voltage detection signal.
The electromagnetic load circuit described above is incapable of diagnosing a failure of a short-circuit of the upstream and the downstream of a switch element in a state where the switch element for holding the injector current to a predetermined current value, i.e., the VB high-side driver 16, has a certain impedance, that is, a layer short-circuit failure.
When a layer short-circuit failure E occurs at a switch element such as a FET comprising the VB high-side driver 16, since full switching cannot be performed in a current holding section, the shunt resistance conductive current drops significantly. However, since a total failure has not yet occurred, a weak current can be applied. Because a layer short-circuit failure is not a complete breakdown, for example, a current passing through the layer short-circuit failure may be neither excessively large nor excessively small and has conventionally been considered difficult to diagnose.
An abnormality detection apparatus capable of detecting a layer short-circuit of an electromagnetic load focuses on a reduction of the period of time required to reach a peak current threshold in the event of a layer short-circuit, and involves detecting a layer short-circuit by detecting an overcurrent using a current detecting circuit installed on a high-side driver switch element (for example, Patent Document 2).
However, the abnormality detection apparatus performs layer short-circuit detection of an electromagnetic load and is not intended to detect a layer short-circuit of a switch element. Therefore, the abnormality detection apparatus is incapable of detecting a layer short-circuit of a switch element.
In addition, there is an abnormality detection apparatus that detects GND short-circuit or open-circuit abnormalities with respect to the downstream of an electromagnetic load (for example, Patent Document 3).
However, this abnormality detection apparatus is similarly not intended to detect an occurrence of a layer short-circuit at a switch element and is incapable of detecting a layer short-circuit of a switch element.
A layer short-circuit of a switch element is not a total failure and is therefore difficult to identify, and as things stand, a failure in an electromagnetic load circuit including a switch element cannot be precisely identified. This problem not only applies to injector circuits of internal-combustion engines, but also applies to electromagnetic load circuits in general.    Patent Document 1: JP Patent Publication (Kokai) No. 2004-124890 A    Patent Document 2: JP Patent Publication (Kokai) No. 2002-176346 A    Patent Document 3: JP Patent Publication (Kokai) No. 2004-347423 A